A television image or picture is defined by a certain number of parameters that represent the spatial and temporal analysis of this image (in particular, the number of images per second, lines per image and pixels per line).
The passband necessary to transmit an HDTV image may attain values of the order of 100 MHz. Thus, to transmit these images on passband channels with reduced width (for example, satellite channels with a band of the order of about ten megahertz), it is necessary to apply passband reduction techniques to these images.
The passband of the signal to be transmitted can be reduced by using adaptive techniques for filtering the high definition image. This filtered high definition image then has a reduced basic passband and may be re-sampled at lower frequencies for transmission. As the filterings are selected in an adaptive way at the transmitter, assistance data are transmitted to the decoder so that it recognizes the processing chosen at the encoder.
These items of assistance data therefore consist of an indicator of the chosen processing, but may also include motion vectors when motion compensation is used.
The throughput rate of the assistance data in the transmission channel is limited to about 1 Mbit/s.
The large quantity of information that these items of data represent makes it necessary to use throughput reduction techniques.
There is a method for the encoding of assistance data described in the conjoint French patent application filed on the same date on behalf of the present applicants, concerning a "method for the encoding of data for assistance in the reconstruction of sub-sampled, moving electronic images."
A characteristic of the encoding of assistance data by this method using the hierarchical code is that it has a variable throughput rate, whereas the throughput rate of the channel is fixed. The regulation of the throughput rate of data leaving the AD (assistance data) encoder therefore proves to be indispensable.
It would seem that no method has been proposed to date.
It is an object of the invention to provide a solution to this problem.